Reason for MINI R56 Engine Startup Noises
I believe the new 2007+ R56 MINI startup noises are due to a similar mode that VW uses to heat up the Cats when cold starting. Here is a paragraph from a VW Document.
The 2.0L turbo operates in two modes. Cold-start conditions initiate a dual-injection mode for rapid heating of the dual catalytic converters. A quantity of fuel is injected on the intake stroke around 300 degrees BTDC of ignition, and the fuel distributes itself homogenously because of the long gap before ignition. A second injection, around 60 degrees BTDC of ignition during the compression phase, forms a rich mixture around the spark plug, which allows a considerable degree of retarded timing without affecting the engine’s stability. Normal mode and stoichometric levels begin quickly, when the catalytic converters have reached operating temperature, usually within 30-40 seconds.
So basically you get two firings of the injectors and some other funny stuff going on.